The problem is that you are attempting to register an anonymous function using spl_autoload_register(), but as you told that you are using PHP5.2 on your web server.
Unfortunately PHP < 5.3 does not support anonymous functions. You need to write a "regular" function:
function my_autoload($class) {
require_once 'classes/' . $class . '.php';
}
spl_autoload_register('my_autoload');
This will work on PHP >= 5.3 as well.
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